The broad, long-term goal of this project is to develop a system for continuous production of biologically active factors which block mucosal infections. The applicant proposes the development of genetically engineered strains of the commensal organism, Streptococcus gordonii, which expresses Porphyromonas gingivalis fimbrillin polypeptides capable of blocking adherence, and of inducing a protective immune response. The specific aims are: (1) to further characterize the expression system recently developed in our laboratory for P. gingivalis fimbrillin on the surface of S. gordonii; (2) to optimize a secretion system in S. gordonii for the production of P. gingivalis fimbrillin; and (3) to test these genetically engineered strains of S. gordonii in the rat model of periodontal disease for reduction of colonization with P. gingivalis and for protection against destructive periodontitis. S. gordonii was selected since it is a non-pathogenic commensal organism, universally found in the human oral cavity, and strains have been genetically engineered to express foreign antigens. P. gingivalis is an important pathogen in a well-established model of mucosal infection, periodontal disease, and its fimbrillin subunit was selected since it has been cloned and sequenced. Furthermore, P. gingivalis fimbrillin domains involved in adherence and in the immune response have been determined. Recombinant S. gordonii strains have been generated that express biologically active domains of fimbrillin and have shown that they are able to generate fimbrillin-specific immune response in rats following oral colonization as well as after parenteral immunization. Rats infected with P. gingivalis were selected as a model of mucosal infection in which to study the early steps in the disease process, namely adherence and colonization, since it is well characterized and provides a useful model to assess in vivo efficacy of a genetically engineered commensal organism producing factors which interfere with virulence. Therefore, studies are proposed to generate recombinant strains of S. gordonii able to either secrete or surface express important fimbrillin peptides, and capable of modulating P. gingivalis infection in a rat model of periodontal disease. Such genetically engineered strains of S. gordonii expressing fimbrillin peptides may be used as a vaccine against P. gingivalis infection, and as a model to study this novel approach to vaccines for other mucosal infections. The model can also be used for evaluating the utility of continuously expressed biologically active molecules by commensal organisms, directed to block colonization and other key early stages in the pathogenesis of mucosal infections.